A diagnostic technique used to obtain cross-range radiation centersfrom antenna patterns

A diagnostic technique for obtaining cross-range radiation centers based on antenna radiation patterns is presented. The method is similar to the synthetic aperture processing of scattered fields normally associated with radar applications; however, in this case it is applied to evaluate antenna radiation pattern performance. Coherence processing of the radiated fields is used to determine the various radiation centers associated with the far-zone pattern of an antenna for a given radiation direction. The technique can be used to identify an unexpected radiation center that creates an undesired effect in a pattern. It can also be used to improve a numerical simulation of the pattern by identifying other significant mechanisms. Cross-range results for two 8-ft-diameter reflector antennas are presented to illustrate as well as validate this technique     

Scattering properties and mutual coupling of antennas with prescribed radiation pattern

An analysis is presented of the interrelations among the radiative, scattering, and coupling properties of arbitrary lossless antennas. The analysis is based on a well-known scattering representation of antennas in terms of spherical modes in free space. This scattering representation is given a network interpretation which brings into focus the degree of interdependence between scattering and radiation characteristics. The scattering matrix of a reciprocal antenna with one port and a prescribed radiation pattern is represented in a canonical form which exhibits explicitly the permissible range of adjustments in the antenna scattering characteristics. The significance of the canonical form is examined from several points of view, noting in particular its connection with the concept of resonant modes of a scatterer. The network interpretation also facilitates the evaluation of mutual coupling, and the mutual impedance between two antennas is expressed explicitly in terms of the radiative and scattering parameters of each antenna. It is shown that, generally, the mutual impedance may be expressed as a sum of two terms: a zeroth-order term, dependent exclusively on the radiation pattern, and a second term involving the scattering properties as well as the radiation patterns. Under certain conditions the mutual impedance may be approximated by the zeroth-order term alone. It is also shown that a similar zeroth-order approximation of the active impedance in an infinite planar phased array leads to a grating lobe series type of representation.     

An Alternative Setup for a Base-Station Cellular Antenna

This paper proposes the use of an alternative setup of a cellular base-station antenna with the potential of reducing the cochannel interference. The setup uses a different cell antenna placement strategy where there is one base-station antenna per cell located high at its center. Unlike a traditional base-station antenna radiating in the horizontal direction, the antenna under consideration radiates downward. The beamwidth of the antenna is considered to be wide enough to match the cell diameter. In addition, the radiation pattern beyond the associated beamwidth is assumed to possess a large attenuation. This paper studies the use of the proposed antenna setup by examining the cell geometry and grouping and its effect on the antenna radiation pattern. It is shown that for a sufficiently large attenuation pattern beyond the antenna beamwidth, the corresponding signal-to-interference ratio can be made significantly larger than the one resulting from the traditional antenna setup     

Three‐dimensional radiation pattern measurement strategy for ground station antennas

This article describes how to measure a three‐dimensional antenna radiation pattern and the most effective method to achieve this. We present a new automated three‐dimensional measurement scheme, inspired by the seed pattern of a sunflower seed head, where the seed placements are arranged in a way so that rotational symmetry is obtained to compromise the circular shape of a dish antenna radiation pattern in the three‐dimensional space. This new AU–TUM Antenna Radiation Measurement Strategy has produced superior results. It has been shown by this scheme that for instance the three‐dimensional transmission pattern of a dish antenna can be measured automatically and easily checked against present regulations. The generic AU–TUM Antenna Radiation Measurement Strategy was verified on a 4.8‐m Ka‐band dish antenna. It was concluded that a three‐dimensional radiation pattern can be measured two to thirteen times faster than the best performing current strategies. Copyright © 2012 John Wiley & Sons, Ltd.     

Scanning synthetic radiation pattern antennas

It is proposed conception of development of new type transmitting-receiving scanning antennas, which are called antennas with synthetic radiation pattern. It is based on application of movement of radiating (receiving) element together with synthesizing of radiation pattern (RP) by means of SAR for processing of recorded information about radiated and received signals. Physical radiator movement can be real or virtual (switching of radiation phase center) due to switching in turns of radiators of one-dimension antenna array (AA) to single-channel transmitter-receiver. There are represented two applications of this approach realization, such as spiral-waveguide slot and tape-slot scanning synthetic RP antennas for registration of radio images and radiofilms in 8-mm wavelength band.     

Simple reconfigurable antenna with radiation pattern

A radiation pattern reconfigurable antenna is proposed. By controlling the switch states, the antenna can be worked as a monopole antenna with an omnidirectional radiation pattern or a dipole antenna with reflector, which has directional radiation pattern. Detailed design considerations of the proposed antenna, simulated and experimental results are presented and discussed.     

Antenna array pattern correlation and input type

When mutual coupling is present in an antenna array, the radiation patterns of the active elements as well as the pattern correlations depend on the representation of the input signal in terms of the input type. The pattern correlation is presented for different input types, i.e. for voltages, currents and voltage waves. It is shown for a microstrip array that a suitable choice of the reference plane of input voltages and currents can lead to a lower pattern correlation than for voltage waves.     

Design and Analysis of a 3-Arm Spiral Antenna

A novel 3-arm spiral antenna structure is presented in this paper. This antenna similar to traditional two-arm or four-arm spiral antennas exhibits wideband radiation characteristic and circular polarization. Advantages offered by the new design are two fold. Unlike the traditional spiral antennas the three-arm spiral can be fed by an unbalanced transmission line, such as a coaxial line or coplanar waveguide, and therefore an external balun is not needed at the feed point. Also by proper choice of arms' dimensions the antenna can be directly matched to any practical transmission line characteristic impedance and therefore external matching networks are not required. This is accomplished by feeding the antenna at the outer radius by a coplanar waveguide (CPW) transmission line and tapering it towards the center. The antenna can also be fed from the center using a coaxial or CPW line perpendicular to the plane of the spiral antenna. A full-wave numerical simulation tool is used to optimize the geometry of the proposed 3-arm spiral to achieve a compact size, wide bandwidth operation, and low axial ratio. The antenna is also designed over a ground plane to achieve a unidirectional radiation and center loading is examined that improves the axial ratio. Simulated results like return loss, radiation pattern, gain, and axial ratio are compared with those obtained from measurements and good agreements are shown. Because of its unique feed structure and compact size, application of the proposed 3-arm spiral antenna for wideband array applications is demonstrated     

柱面共形蝶形微带天线的阻抗特性和方向图研究

研究了小曲率半径有限长度圆柱体上共形蝶形微带天线的阻抗特性和方向图.给出了不同曲率半径下的柱面共形蝶形微带天线反射损失和方向图的仿真结果.实际制作和测试了柱面共形微带天线的单元和二元阵列天线,仿真结果与实测结果比较吻合.研究表明:当圆柱半径较小时,不但方向图改变,而且谐振频率下降、阻抗带宽明显减小;当圆柱长度缩短时,方向图的起伏增大.     

The simultaneous interpolation of antenna radiation patterns inboth the spatial and frequency domains using model-based parameterestimation

The Pade rational function fitting model commonly used for model-based parameter estimation (MBPE) in the frequency domain is enhanced to include spatial dependence in the numerator and denominator coefficients. This allows the function to interpolate an antenna radiated electric field pattern in both the frequency and spatial domains simultaneously, such that a single set of coefficients can be used to accurately reconstruct an entire radiation pattern at any frequency in the fitting-model range. A simple procedure is introduced for transforming interpolated electric fields into gain patterns using input impedance versus frequency curves also obtained via MBPE. The utility of this method is demonstrated by applying it to a dipole antenna over a frequency range of 150-950 MHz and using a polynomial representation in &thetas; for the coefficient spatial dependence. It is also used to estimate radiation patterns for a three-element Yagi array between the frequencies of 470 and 500 MHz using a binomial representation for the spatial variation that includes terms dependent on &thetas; as well as φ. The use of this method for interpolating radiation patterns has at least two significant advantages; one being large compression ratios for the amount of data that must be stored to accurately reproduce patterns and the other being a significant decrease in the amount of time required for modeling problems with large computational domains     

Log-periodic antenna with unidirectional radiation characteristics

The properties of an inclined form of a planar log-periodic antenna are described. The planar antenna has radiation characteristics similar to those of a halfwavelength dipole, but with a bandwidth as large as desired. It is shown that, when the planar antenna is inclined about one axis of symmetry, the resulting structure has unidirectional radiation patterns.     

A phase-space beam summation formulation for ultrawide-band radiation

A new discrete phase space Gaussian beam (GB) summation representation for ultrawide-band (UWB) radiation from an aperture source distribution is presented. The formulation is based on the theory of the windowed Fourier transform (WFT) frames, wherein we introduce a novel relation between the frequency and the frame overcompleteness. With this procedure, the discrete lattice of beams that are emitted by the aperture satisfies the main requirement of being frequency independent, so that only a single set of beams needs to be traced through the medium for all the frequencies in the band. It is also shown that a properly tuned class of iso-diffracting (ID) Gaussian-windows provides the "snuggest" frame representation for all frequencies, thus generating stable and localized expansion coefficients. Furthermore, due to the ID property, the resulting GBs propagators are fully described by frequency independent matrices whose calculation in the ambient environment need to be done only once for all frequencies. Consequently, the theory may also be expressed directly in the time-domain as will be presented elsewhere. The localization implied by the new formulation is demonstrated numerically for an UWB focused aperture. It is shown that the algorithm extracts the local radiation properties of the aperture source and enhances only those beams that conform with these properties, i.e., those residing near the phase space Lagrange manifold. Further localization is due to the fact the algorithm accounts only for beams that pass within a few beamwidths vicinity of the observation point. It is thus shown that the total number of beams is much smaller than the Landau Pollak bound on the aperture's degrees of freedom.     

X波段微波全息天线的仿真与设计

本文介绍了一种基于光学全息理论的全息天线,并通过仿真对全息天线工作原理进行了验证,结论表明如果在介质板上形成不同的干涉图案,就可以实现天线最大辐射方向的扫描。     

Beam-Switching Antenna Based on Plane Dipole Structure

A novel method for designing a beam-switching antenna with the plane dipole is presented. The antenna is composed of double dipoles placed at the center of an active square structure that is divided in four equal sectors by metallic sheets. Metallic patches at the outside of the structure are used to enhance the radiation performance of the antenna. In each step, the diodes in one sector are on, whereas other diodes are off. The sector with off-state diodes defines the direction of the radiation pattern. An antenna model is designed on the substrate of FR4. The proposed antenna operates from 4.8 GHz to 5.5 GHz with gain of 6.3 dBi and F/B (front to back ratio) of 13.2 dBi when the operating frequency is 5.2 GHz. The antenna radiation pattern can be swept in the entire azimuth plane in four steps with a 3 dB beamwidth of 90. The results reveal that the antenna could be used in the base station of the wireless communication systems.     

The Ultrawideband Leaky Lens Antenna

A novel directive and nondispersive antenna is presented: the ultrawideband (UWB) leaky lens. It is based on the broad band Cherenkov radiation occurring at a slot printed between different infinite homogeneous dielectrics. The first part of the paper presents the antenna concept and the UWB design. The issues that are specifically addressed include the impedance matching, the radiation pattern and the phase purity. Subsequently the hardware demonstrator and the results of the measurement campaign are shown. The results fully validate the antenna concept. The antenna presents decade bandwidth impedance matching, directive and frequency independent patterns in the H-plane over two octaves, negligible cross-polarization levels, weak amplitude dispersivity and, according to the authors, the most stable phase center for a directive antenna over an ultra wide frequency range.     

Space wave radiation efficiency of a wraparound antenna and theeffect of surface wave radiation due to the dielectric substratetruncation

A theoretical study of the problem of excitation of surface waves in wraparound microstrip antennas is presented. The surface waves are obtained by using a contour integral in the complex plane. The surface-wave energy loss in the antenna truncation region is partially radiated and interfaces with the space wave. The radiation efficiency and the effect of the dielectric substrate truncation of the antenna radiation pattern are shown as functions of antenna dimensions and for two values of substrate dielectric constants     

The radiation from rectangular microstrip antennas mounted on two-dimensional objects

The radiation patterns for a quadratic microstrip antenna mounted on two-dimensional objects, the circular cylinder and the strip, have been calculated using both the transmission-line model and the resonator model. Analytical expressions for the far field are presented, and calculations are compared with measurements. All measurements clearly indicate that the resonator model is better than the transmission-line model in radiation pattern calculations outside the principal planes of the antenna.     

A new design of horizontally polarizedand dual-polarized uniplanar conical beam antennas for HIPERLAN

It is shown that a conical beam 5.2-GHz antenna suitable for HIPERLAN application, but working in horizontal polarization, can be realized as a group of microstrip patch radiators in a ring formation. Layouts with three and four patches are described, and radiation patterns are found to agree well with predictions from a simple array model. The three-patch form is smaller and gives a closer approximation to an azimuth-independent pattern. Patterns are very similar to those achieved in vertical polarization with previously reported disk antenna realizations, giving peak radiation at about 50/spl deg/ elevation. Two methods of impedance matching are found to give satisfactory results. A dual-polarized conical-beam microstrip antenna, with a strictly uniplanar conductor pattern, is also presented and realized as an array of three square patches whose corners meet a central feed point. For the second polarization, the antenna functions as a series fed array. Fairly good conical beam patterns have been obtained, though only moderate polarization purity appears to be obtainable from three-element arrays.     

Bow-tie antennas on a dielectric half-space: Theory and experiment

A new formulation is discussed for the rigorous calculation of the radiation pattern of a bow-tie antenna of finite length and infinitesimal thickness, placed on a lossless dielectric substrate. The analysis is based on a representation of the current density on the metal surface of the antenna as a sum of an imposed (quasistatic) term and a set of current modes with unknown amplitudes. Free-space fields that are expressed in terms of continuous spectra of symmetrized plane waves are matched to the current modes using the method of moments. The resulting set of equations are solved for the unknown current amplitudes. The calculations show that for increasing bow length the antenna impedance spirals rapidly to a value predicted by transmission line theory. The theory also shows that theE-plane pattern of a two wavelength,60degbow-tie antenna is dominated by low-loss current modes propagating at the dielectric wavenumber. As the bow tie narrows, the loss of the modes increases, and the dominant wavenumber tends to the quasistatic value. Pattern measurements made at 94 GHz are shown to agree well with theoretical predictions. Measurements for a long-wire antenna, a linear array of bow-tie elements, and a log-periodic antenna are also presented.     

Resonance and radiation of a superstrate-loaded spherical-circularmicrostrip patch antenna

The effects of the dielectric superstrate cover on the resonance and radiation problems of a spherical-circular microstrip patch antenna are studied, using the Green's function formulation in the spectral domain and the Galerkin moment method calculation. Numerical results for the resonant frequency, half-power bandwidth, and radiation pattern of the superstrate-loaded antenna are presented. The effects of curvature on these characteristics are also shown